JP2023071440A - Particle beam therapy system, irradiation control device, and irradiation control method - Google Patents

Abstract

To provide a particle beam therapy system that can more accurately control the dose of a particle beam with which a subject is irradiated.SOLUTION: A dose monitor 202 measures the dose of a beam 160. A position monitor 203 measures the beam size of the beam 160. An irradiation control device 108 calculates a measurement characteristic of the dose monitor 202 on the basis of the dose and the beam size of the beam 160, and controls the irradiation of a patient 150 with the beam 160 on the basis of the measurement characteristic and the dose.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a particle beam therapy system, an irradiation control device, and an irradiation control method.

In recent years, particle beam therapy that irradiates a patient's tumor with particle beams such as proton beams and carbon beams has attracted attention. Compared to X-ray therapy, particle beam therapy uses a phenomenon called a black peak, in which a large dose of radiation is applied to the surrounding area just before the particle beam stops. Therefore, the realization of highly accurate radiotherapy is expected.

In particle beam therapy, a charged particle beam (hereinafter simply referred to as a particle beam) accelerated by an accelerator system with a linear accelerator or synchrotron, etc. is transported as a particle beam to an irradiation nozzle and irradiated toward the tumor in the patient's body. do. Main beam irradiation methods include a passive method and a scanning method. The passive method is a method of matching the shape of the particle beam to the shape of the tumor by enlarging the beam diameter using a scatterer, ridge filter, collimator, patient bolus, or the like. The scanning method adjusts the irradiation direction of a thin particle beam called a pencil beam with a scanning electromagnet called an irradiation nozzle inside a container, and creates multiple microscopic areas (hereinafter referred to as spots) virtually set within the tumor. By irradiating each of them in turn, it is a method of irradiating the entire tumor with a particle beam. Scanning methods include a spot scanning method in which spots are moved while the particle beam is stopped, and a raster scanning method in which spots are moved while the particle beam is being irradiated. In recent years, the number of facilities adopting the scanning method is increasing because it is possible to deal with complicated tumor shapes and their changes.

In the scanning method, the particle beam is monitored by a position monitor and dose monitor installed in the irradiation nozzle, and the irradiation dose is controlled for each spot based on the monitoring results. A position monitor measures the center position and size of the particle beam, and a dose monitor measures the dose magnitude. The irradiation control device calculates the integrated dose, which is the integrated value of the irradiation dose irradiated to the spot, from these measured values, and the integrated dose reaches the target dose (hereinafter referred to as the prescription) set in advance for each spot. Then, the next spot is irradiated with the beam. Therefore, high measurement accuracy is required for the position monitor and the dose monitor in order to prevent damage to surrounding healthy tissue while applying a sufficient dose to the tumor.

However, the dose monitor is known to have a problem that the dose rate, which is the dose detected per unit time, affects the measurement accuracy. An ionization chamber, which is a general dose monitor, is a container in which the gaps between multiple electrodes are filled with a fluid such as gas or liquid. and electrons are generated. By applying a voltage between the electrodes, the cations and electrons move to the opposite electrodes, causing a short current to flow between the electrodes. The dose is calculated by measuring this current. However, as the dose rate increases, the density of generated cations increases, so the rate of recombination of cations and electrons before reaching the electrode increases, and the dose monitor collects cations and electrons. Collection efficiency decreases.

In conventional particle beam therapy, since the dose rate is relatively small, the reduction in the collection efficiency of the dose monitor is about 1%, and the influence on the linear responsiveness of the dose monitor is small. However, in recent years, radiation therapy with an ultra-high dose rate called FLASH radiation therapy has attracted attention, and the demand for radiation with a higher dose rate than in the past is increasing. Under a high dose rate, the collection efficiency of the ionization chamber may decrease by several tens of percent, in which case the linear response of the dose monitor will collapse. Therefore, in order to control the dose given to the subject with high accuracy, it is required to grasp the collection efficiency of the dose monitor.

Patent Literature 1 discloses a technique for correcting the collection efficiency of an ionization chamber based on a prescription prepared in advance. In this technique, the dose rate and size of the beam irradiated to the patient during treatment are estimated as beam parameters based on the prescription. Based on the beam parameters, a correction factor is determined for each spot to correct the preset collection efficiency.

Patent No. 6807125

However, since the beam parameters fluctuate during the irradiation of the particle beam, the beam parameters estimated based on the prescription do not necessarily match the beam parameters of the actually irradiated particle beam. In particular, in particle beam irradiation at a high dose rate, the fluctuation of beam parameters is so large that it cannot be ignored. For this reason, the technique described in Patent Document 1 cannot appropriately correct the collection efficiency of the dose monitor, and it is difficult to accurately control the dose of the particle beam irradiated to the subject.

The present disclosure has been made in view of the above circumstances, and provides a particle beam therapy system, an irradiation control device, and an irradiation control method capable of more accurately controlling the dose of a particle beam irradiated to a subject. for the purpose.

A particle beam therapy system according to an aspect of the present disclosure is a particle beam therapy system that irradiates a subject with a particle beam, comprising a dose monitor that measures the dose of the particle beam, and a beam size of the particle beam that measures calculating a measurement characteristic obtained by correcting the measurement characteristic of the dose monitor based on the position monitor, the dose and the beam size, and irradiating the subject with the particle beam based on the measurement characteristic and the dose and an irradiation control device that controls the

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to control more correctly the dose of the particle beam irradiated to a subject.

1 is a diagram showing the overall configuration of a particle beam therapy system according to Example 1 of the present disclosure; FIG. FIG. 2 is a diagram showing the configuration of an irradiation nozzle according to Example 1 of the present disclosure; It is a figure which shows an example of a structure of the dose monitor of Example 1 of this indication. 1 is a diagram illustrating an example of a configuration of a position monitor according to Example 1 of the present disclosure; FIG. FIG. 4 is a diagram for explaining an example of a method of calculating the center position and size of a beam according to the first embodiment of the present disclosure; FIG. 4 is a flowchart for explaining the operation of particle beam therapy according to Example 1 of the present disclosure; 1 is a diagram illustrating a configuration example of an irradiation control system according to Example 1 of the present disclosure; FIG. 6 is a flowchart for explaining an example of monitoring processing according to the first embodiment of the present disclosure; FIG. 4 is a conceptual diagram of a collection efficiency table according to Example 1 of the present disclosure; FIG. 10 is a diagram showing an example of a first spot determination method in Example 2 of the present disclosure; FIG. 10 is a diagram showing the configuration of an irradiation control system according to Example 2 of the present disclosure; FIG. 10 is a flowchart for explaining an example of monitoring processing according to the second embodiment of the present disclosure; FIG.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

First, a particle beam therapy system and an irradiation control apparatus according to a first embodiment of the present disclosure will be described with reference to FIGS. 1 to 9. FIG.

FIG. 1 is a diagram showing the overall configuration of the particle beam therapy system of this embodiment. A particle beam therapy system 100 shown in FIG. 1 is a system that irradiates a beam 160, which is a particle beam, to a patient 150, who is a subject. In this embodiment, the particle beam therapy system 100 uses a spot scanning method or a raster scanning method for sequentially irradiating spots, which are a plurality of virtually minute areas set inside the body of the patient 150 .

The particle beam therapy system 100 includes, as shown in FIG. A transport system control device 107 and an irradiation control device 108 are provided.

Accelerator system 101 is a group of devices that generate and emit beam 160 . In the example of FIG. 1, the accelerator system 101 has an ion source 111 , an injector 112 and a synchrotron accelerator 113 . The ion source 111 produces charged particles, which are the originating particles of the beam 160 . The injector 112 injects the charged particles generated by the ion source 111 into the synchrotron accelerator 113 . The synchrotron accelerator 113 accelerates charged particles injected from the injector 112 to generate and output a beam 160 .

Note that the accelerator system 101 shown in FIG. 1 is merely an example and is not limited to this example. For example, the accelerator system 101 may be a device group using a cyclotron accelerator or a synchrocyclotron accelerator instead of the synchrotron accelerator 113 .

The beam transport system 102 is a device group that transports the beam 160 emitted from the accelerator system 101 to the irradiation nozzle 103 . The beam transport system 102 has a beam path 121 and a bending electromagnet 122 . A beam path 121 is a path through which the beam 160 passes, and connects the accelerator system 101 and the irradiation nozzle 103 . Beam path 121 is in a vacuum. The bending electromagnet 122 deflects the beam passing through the beam path 121 with a magnetic field and transports it to the irradiation nozzle 103 . The beam transport system 102 may or may not have a rotating gantry that adjusts the irradiation angle for irradiating the patient 150 with the beam 160 .

The irradiation nozzle 103 includes a device group including a device for irradiating the patient 150 with the beam 160 transported from the beam transport system 102 and a device for measuring beam parameters, which are parameters related to the beam 160. is the body. A more detailed configuration of the irradiation nozzle 103 will be described later using FIG.

Treatment table 104 is a bed on which patient 150 is placed. The treatment table 104 moves based on instructions from the overall control device 106 to move the position and posture (angle) of the patient 150 to a desired position and posture. The treatment table 104 can move in six axial directions including, for example, translational movement along each of three axes facing in mutually different directions and rotational movement about each of the three axes as a rotation axis. be.

The treatment planning device 105 draws up a treatment plan for the patient 150 , prepares a prescription, and transmits the prescription to the overall control device 106 . The prescription indicates, for each spot irradiated with the beam 160, a target dose, which is a target value of the dose of the beam 160 irradiated to that spot.

The general control device 106 is connected to the treatment table 104, the treatment planning device 105, the accelerator/beam transport system control device 107, and the irradiation control device 108, and controls each connected device based on the prescription from the treatment planning device 105. do.

The accelerator/beam transport system controller 107 controls the accelerator system 101 and the beam transport system 102 based on instructions from the overall controller 106 .

The irradiation control device 108 controls the irradiation nozzle 103 based on instructions from the overall control device 106 . Further, the irradiation control device 108 processes the measurement results obtained by the irradiation nozzle 103 and transfers them to the overall control device 106 . A more detailed configuration of the irradiation control device 108 will be described later using FIG.

The treatment planning device 105, the overall control device 106, the accelerator/beam transport system control device 107, and the irradiation control device 108 include, for example, a central processing unit (CPU), a memory, a storage device, a communication interface device, and a user interface (UI) device. and the like. Each of these devices performs various processes, for example, by having a central processing unit read and execute a program recorded in a memory. Each device may have a single program, may be divided into a plurality of programs, or may be a combination thereof. Also, part or all of the program of each device may be realized by dedicated hardware, or may be modularized. Also, part or all of the program may be installed in each device using a program distribution server (not shown), an external storage medium, or the like. Also, each device may be configured as an independent device and connected to each other via a wired or wireless network, or may be a device in which two or more devices are integrated.

FIG. 2 is a diagram showing a configuration example of the irradiation nozzle 103. As shown in FIG.

The irradiation nozzle 103 shown in FIG. 2 includes an irradiation system 200 for irradiating a patient 150 with a beam 160, a dose monitor control device 206 which is a control system for controlling the irradiation system 200, a position monitor control device 207, and a scanning electromagnet control device. 208. The irradiation system 200 has scanning electromagnets 201 A and 201 B, a dose monitor 202 and a position monitor 203 .

In addition, the irradiation system 200 may have a ridge filter 204 that expands the black peak of the beam 160 in the traveling direction of the beam 160 and a range shifter 205 that adjusts the depth to which the beam 160 reaches, if necessary. .

The scanning electromagnets 201A and 201B are a scanning system that scans the beam 160 in a plane (two-dimensional direction) perpendicular to the passing direction of the beam 160 . Beam 160 scanned by scanning magnets 201 A and 201 B impinges on target volume 151 within patient 150 . The target volume 151 is an irradiation area irradiated with the beam 160. For example, when the particle beam therapy system 100 treats a tumor such as cancer of the patient 150, a margin (error in the irradiation position is considered) is added to the tumor area where the tumor exists. margin area) is added. The spot irradiated by beam 160 is set within target volume 151 .

The dose monitor 202 is a monitor for measuring the dose rate of the beam 160 applied to each spot. The dose monitor 202 outputs a detection signal indicating the measurement result to the dose monitor control device 206 . The dose monitor control device 206 calculates the dose rate of the beam 160 irradiated to each spot based on the detection signal from the dose monitor 202 and outputs it to the irradiation control device 108 .

FIG. 3 is a diagram showing an example of the dose monitor 202. As shown in FIG. The dose monitor 202 shown in FIG. 3 is a generally used parallel plate ionization chamber.

A dose monitor 202, which is a parallel plate ionization chamber shown in FIG. Specifically, the beam windows 302 are formed at positions facing each other on the shielding wall 301 so that the beam 160 entering from one beam window 302 is emitted from the other beam window. In the space surrounded by the shielding wall 301, one or more flat high-voltage electrodes 303 and one or more flat collector electrodes 304 are arranged in parallel. In the example of FIG. 3, the dose monitor 202 has one high-voltage electrode 303 and two collecting electrodes 304 provided with the high-voltage electrode 303 interposed therebetween. A high voltage is applied to the high voltage electrode 303 and an electric field is generated between the high voltage electrode 303 and the collector electrode 304 . Also, the spaces between the electrodes 303 and 304 are filled with gas.

The beam 160 passing through the beam window 302 and entering the dose monitor 202 ionizes the gas between the electrodes 303-304 to generate positive ions and electrons. The generated cations and electrons move to the collecting electrode 304 by the electric field generated between the electrodes 303-304. This movement of positive ions and electrons causes current 305 to flow between electrodes 303 and 304 and is measured by dose monitor control device 206 .

A proportional relationship exists between the dose of the beam 160 and the amount of ions generated. Therefore, the dose monitor controller 206 calculates the dose rate of the beam 160 from the current 305 by multiplying the value of the current 305 by an appropriate coefficient. The dose rate calculated by the dose monitor control device 206 is the pre-correction dose rate, which is the dose rate that does not consider the fluctuation of the collection efficiency of the dose monitor 202 .

Note that the dose monitor 202 is not limited to the example shown in FIG. For example, the spaces between the electrodes 303 and 304 may be filled with liquid or may be open to the air. Moreover, the shape of each of the electrodes 303 and 304 is not limited to a flat plate shape, and may be, for example, a coaxial cylindrical shape. Also, the dose monitor 202 is not limited to the ionization chamber, and may be any monitor whose measurement characteristics change according to the dose rate and beam size.

Returning to the description of FIG. A position monitor 203 is a monitor for measuring the center position and beam size of the beam 160 . Position monitor 203 outputs a detection signal indicating the measurement result to position monitor control device 207 . The position monitor control device 207 calculates the center position and beam size of each beam based on the detection signal input from the position monitor 203 and outputs them to the irradiation control device 108 .

FIG. 4 is a diagram showing an example of the position monitor 203. As shown in FIG. The position monitor 203 shown in FIG. 4 is a commonly used multi-strip ionization chamber.

The multi-strip ionization chamber, which is the position monitor 203, is covered with a shielding wall (not shown) similar to the dose monitor 202 shown in FIG. A plurality of windows 401 are formed. Specifically, the beam windows 402 are formed at positions of the shielding wall facing each other so that the beam 160 entering from one beam window 402 is emitted from the other beam window. In the space surrounded by the shielding wall, one or more flat high-voltage electrodes 402 and one or more flat collector electrodes 403A and 403B are arranged in parallel. A high voltage is applied to the high voltage electrode 402, and an electric field is generated between the high voltage electrode 402 and the collecting electrodes 403A and 403B. Also, spaces between the electrodes 402, 403A and 403B are filled with a fluid such as gas or liquid.

The collector electrode 403A is composed of a plurality of strip-shaped small collector electrodes arranged in parallel in one in-plane direction (X direction), and the collector electrode 403B is arranged in a direction orthogonal to the X direction in the plane (Y direction). It consists of a plurality of strip-shaped small collector electrodes arranged in parallel with each other.

Beam 160 passing through beam window 401 and entering position monitor 203 ionizes the fluid between electrodes 402-403 to generate positive ions and electrons. The generated cations and electrons move to the adjacent small collector electrodes 304A or 304B due to the electric field generated between the electrodes 402-403. Then, the position monitor control device 207 measures each small collecting electrode. As a result, the position monitor control device 207 can measure the two-dimensional ion generation distribution and thus the dose distribution in the in-plane direction of the collector electrode 304A or 304B based on the current 404 for each small collector electrode. The center position and beam size of beam 160 can be calculated from the dose distribution.

FIG. 5 is a diagram for explaining an example of a calculation method for calculating the center position and beam size of the beam 160. FIG. In FIG. 5, the horizontal axis indicates the center position of each small collector electrode of the collector electrode 403A in the X direction, and the vertical axis indicates the current value. Each data point 501 in FIG. 5 represents the current value indicated by the detection signal of each small collecting electrode.

Assuming that the shape of beam 160 follows Gaussian distribution, peak position 503 and standard deviation 504 when distribution of data points 501 is approximated by Gaussian function 502 are the center position and beam size of beam 160, respectively. Although FIG. 5 shows an example of a one-dimensional distribution for simplicity, in practice, a two-dimensional dose distribution is approximated by a two-dimensional Gaussian function.

Note that the method of calculating the center position and beam size of the beam 160 is not limited to the above example, and assuming that the shape of the beam 160 follows the Lorentzian distribution, the dose distribution may be approximated by the Lorentzian function. . Also, the position monitor 203 is not limited to the example shown in FIG. For example, position monitor 203 may be a multi-wire ionization chamber or the like.

Returning to the description of FIG. The irradiation control device 108 calculates the irradiation position of the beam 160 from the center position of the beam 160 calculated by the position monitor control device 207 . In addition, the irradiation control device 108 calculates the collection efficiency, which is the measurement characteristic of the dose monitor 202, based on the beam parameters (dose rate, center position, and beam size) transmitted from the dose monitor control device 206 and the position monitor control device 207. calculate. The irradiation control device 108 corrects the dose rate calculated by the dose monitor control device 206 based on the collection efficiency, thereby calculating a corrected dose rate in consideration of the fluctuation of the collection efficiency.

Next, operation of the particle beam therapy system 100 will be described.

FIG. 6 is a flowchart for explaining an example of treatment processing for treating a patient 150 with the particle beam therapy system 100. As shown in FIG.

In particle beam therapy, a plurality of beams are usually applied to the patient 150 in order to prevent normal tissues of the patient 150 from being damaged by applying a high-dose beam 160 to the patient 150 at one time. Division irradiation is performed in which the irradiation is divided into times. In this embodiment, the division unit is one day, and the number of divisions is 30. However, the division unit and the number of divisions are not limited to these examples. For example, the fractional units need not be one day, and multiple treatments may be given per day.

First, when treatment on the current day (day d) is started (step S601), the treatment planning device 105 creates a prescription as a treatment plan (step S602). The initial value of d is one.

Specifically, in step S602, the treatment planning apparatus 105 first reads an in-vivo image showing the periphery of the tumor, which is the affected area of the patient 150, and calculates the thickness from the body surface of the patient 150 to the affected area based on the in-vivo image. The thickness distribution is converted to a water equivalent thickness ratio distribution. An in-vivo image is created by, for example, a CT (Computed Tomography) examination. The water equivalent thickness ratio is the ratio of the thickness of water to the thickness of the local medium that causes the same energy loss to the beam 160 and is the physical quantity that determines the stopping distance of the beam 160 .

Subsequently, the treatment planning system 105 uses the in-vivo image to determine the outline of the target volume 151, which is the three-dimensional irradiation area for the beam 160 to be irradiated. For example, the treatment planning device 105 displays an in-vivo image, allows an operator such as a doctor to draw the outline of a tumor, adds a predetermined margin to the outline of the tumor, and determines the outline of the target volume 151 .

Furthermore, the treatment planning device 105 creates a prescription (a target dose set for each spot). Specifically, treatment planning device 105 first sets a target dose for target volume 151 . A target dose is input, for example, by an operator. The treatment planning apparatus 105 calculates the spot position and the target dose for applying the target dose to the target volume 151 based on the distribution of the water-equivalent thickness ratio, using a predetermined optimization calculation method or the like. create a prescription; The treatment planning device 105 displays the prescription, and when the operator approves the prescription, the treatment planning device 105 transmits the prescription to the general control device 106 .

Based on the prescription from the treatment planning device 105, the general control device 106 creates control instruction data for each spot to control the accelerator/beam transport system control device 107 and the irradiation control device 108, and controls the accelerator/beam transport. It is transmitted to the system controller 107 and the irradiation controller 108 . The transmitted data is stored in a memory (not shown) in the accelerator/beam transport system controller 107 and the irradiation controller 108 . The control instruction data for the accelerator/beam transport system controller 107 includes, for example, the excitation current value of each electromagnet of the accelerator system 101 and the beam transport system 102 determined according to the beam energy corresponding to the depth of the spot position, and the high-frequency acceleration space. It includes the high frequency power value applied to the barrel. The control instruction data for the irradiation control device 108 includes the target dose, the current values of the scanning electromagnets 201A and 201B, and the like.

The process of step S602 ends here. If the prescription is not approved by the operator, the target dose is reset.

After that, the patient 150 is placed on the treatment table 104, and the position of the patient 150 is adjusted so as to coincide with the time when the in-vivo image is taken, and the operator instructs the particle beam therapy system 100 to irradiate the beam 160 ( step S603).

Then, the general control device 106 transmits an irradiation start instruction to the spot to be irradiated (assumed to be the n-th spot) to the accelerator/beam transport system control device 107 and the irradiation control device 108 (step S604). The initial value of n is 1.

Upon receiving the irradiation start instruction, the accelerator/beam transport system controller 107 starts accelerating the beam 160 according to the control instruction data stored in the memory. After the acceleration of beam 160 is completed, irradiation control device 108 changes the current values of scanning electromagnets 201A and 201B via scanning electromagnet control device 208 . When the change of the current value is completed, the accelerator/beam transport system controller 107 emits the beam 160 . The emitted beam 160 passes through the beam transport system 102 and the irradiation nozzle 103 and is irradiated onto the target volume 151 of the patient 150 . The dose monitor 202 and the position monitor 203 measure beam parameters of the beam 160, and the irradiation control device 108 calculates the dose of the beam 160 for the n-th spot based on the beam parameters (step S605).

After that, when the dose reaches the target dose, the irradiation control device 108 sends an end signal to the general control device 106 indicating the end of irradiation of the beam 160 to the nth spot. Upon receiving the end signal, the general controller 106 executes end processing for ending the irradiation of the beam 160 to the n-th spot (step S606). The termination process is a process of stopping the irradiation of the beam 160 when the spot scanning method in which the spots are moved while the beam is stopped is adopted. When the scanning method is employed, this is the process of preparing for irradiation of the next spot.

Then, the overall controller 106 determines whether or not irradiation of the last spot with the beam 160 has ended (step S607).

If irradiation of the beam 160 to the last spot has not been completed, the general controller 106 increments n and instructs the accelerator/beam transport system controller 107 and the irradiation controller 108 to irradiate the next spot. Preparation is instructed (step S608), and the process returns to step S604.

On the other hand, when irradiation of the last spot with the beam 160 ends, the treatment for the day ends. Then, the overall control device 106 determines whether it is the last day. If it is not the last day, the process of step S601 is executed, and if it is the last day, the process ends.

The irradiation control device 108 may be directly connected to the accelerator/beam transport system controller 107 to directly transmit various signals to the accelerator/beam transport system controller 107 .

In the following, the irradiation dose monitoring process, which is the process of steps S604 to S606 in FIG. 6, will be described in more detail.

FIG. 7 is a diagram showing a configuration example of an irradiation control system including the irradiation nozzle 103 and the irradiation control device 108. As shown in FIG. FIG. 8 is a flowchart for explaining an example of monitoring processing by the irradiation control system shown in FIG. In the following, the irradiation of the beam 160 to the n-th spot will be described as an example.

As shown in FIG. 7, the dose monitor control device 206 includes an I/F converter 702 that converts the current output from the dose monitor 202 into a pulse signal, and based on the pulse signal converted by the I/F converter 702, and a CPU 705 for calculating the dose rate. Note that the pulse frequency of the pulse signal represents the dose rate. The position monitor control device 207 includes an I/F converter 704 that converts the current output from the position monitor 203 into a pulse signal, and based on the pulse signal converted by the I/F converter 704, the center position of the beam 160 and and a CPU 706 for calculating the beam size.

The irradiation control device also has a memory 701 for storing control instruction data (target dose of each spot) and a CPU 707 . The CPU 707 also has a counter 703 that counts the number of pulses.

When step S604 is started, the general control device 106 first transmits an irradiation start instruction to the accelerator/beam transport system control device 107 and the irradiation control device 108 (step S801). Upon receiving the irradiation start instruction, the accelerator/beam transport system controller 107 accelerates and emits the beam 160 according to the control instruction data stored in the memory (step S803).

The CPU 707 of the irradiation control device 108 stores the memory The target dose corresponding to the n-th spot among the target doses stored in 701 is read. In this embodiment, the current output from the dose monitor 202 is converted into a pulse signal by the I/F converter 702 of the dose monitor control device 206, and the pulse number of the pulse signal represents the dose. is converted into the target number of pulses converted into the number of pulses and set in the counter 703 (step S802).

A conversion factor for converting the target dose to the target number of pulses is determined according to the characteristics of the dose measurement circuit including the dose monitor 202 and I/F converter 702 . Note that the process of step S802 may be performed between the completion of the irradiation of the beam 160 for the previous spot (n−1-th spot) and the transmission of the irradiation start instruction for the spot.

Then, when the beam 160 is emitted (step S803), the currents detected by the dose monitor 202 and the position monitor 203 during irradiation of the target volume 151 by the beam 160 are applied to the dose monitor controller 206 and the position monitor control unit 206, respectively. It is converted into a pulse signal by I/F converters 702 and 704 in device 207 . The CPU 705 of the dose monitor control device 206 calculates the dose rate of the beam 160 from the pulse signal and transmits it to the irradiation control device 108, as described with reference to FIG. 4, the CPU 706 of the position monitor control device 207 calculates the center position and beam size of the beam 160 from the two-dimensional distribution of the pulse frequency of the pulse signal and transmits them to the irradiation control device 108. (Step S804). The conversion factor for converting the current into the pulse signal is a constant determined according to the characteristics of the dose measuring circuit, like the conversion factor for the target dose.

The CPU 707 of the irradiation control device 108 calculates the collection efficiency of the dose monitor 202 with respect to the beam 160 based on the dose rate and beam size (step S805).

As an example of the collection efficiency calculation method, a calculation method based on a theoretical formula will be described below.

一方、線量モニタ２０２にて測定される積算ビーム電流Ｊは、線量モニタ２０２内の微小領域におけるビーム電流密度ｉ（ｒ）及び局所収集効率ｆ（ｒ）を用いて以下の式２で表される。

Ｂｏａｇの理論によると、局所収集効率ｆ（ｒ）とビーム電流密度ｉ（ｒ）とは、式３で示される関係を有する。

ここで、ｋは２．０１×１０^７［Ｖ／（ｍ^０．５Ａ^０．５）］であり、Ｖは線量モニタ２０２に印加する印加電圧であり、ｄは線量モニタ２０２の構造によって決定される定数であり、例えば、線量モニタ２０２が１つの高圧電極３０３と１つの集電極３０４とで構成される場合には、高圧電極３０３と集電極３０４との間隔である。式１及び式３を式２に代入して積分することで、線量モニタ２０２全体における収集効率Ｆは、積算ビーム電流Ｊの関数として式４で表される。

積算ビーム電流Jは、線量モニタ制御装置２０６にて算出された線量率に一定の係数を積算することで求められ、ビームサイズσは位置モニタ制御装置２０７にて算出される。したがって、照射制御装置１０８のＣＰＵ７０７は、これらの値を数４に代入することで、収集効率Ｆを算出することができる。 Assuming that the divergence of beam 160 follows a Gaussian distribution, the beam current density i(r) of beam 160 at distance r from the center of beam 160 is: is described by Equation 1 of Note that the distance r is the distance in the plane perpendicular to the traveling direction of the beam 160 .

On the other hand, the integrated beam current J measured by the dose monitor 202 is expressed by the following equation 2 using the beam current density i(r) and the local collection efficiency f(r) in the minute area within the dose monitor 202. .

According to Boag's theory, the local collection efficiency f(r) and the beam current density i(r) have the relationship shown in Eq.

where k is 2.01×10 ⁷ [V/(m ^0.5 A ^0.5 )], V is the applied voltage applied to dose monitor 202, and d is determined by the structure of dose monitor 202. For example, when the dose monitor 202 is composed of one high-voltage electrode 303 and one collector electrode 304 , it is the interval between the high-voltage electrode 303 and the collector electrode 304 . By substituting Equations 1 and 3 into Equation 2 and integrating, the collection efficiency F in the entire dose monitor 202 is expressed as Equation 4 as a function of the integrated beam current J.

The integrated beam current J is obtained by multiplying the dose rate calculated by the dose monitor control device 206 by a constant coefficient, and the beam size σ is calculated by the position monitor control device 207 . Therefore, the CPU 707 of the irradiation control device 108 can calculate the collection efficiency F by substituting these values into Equation (4).

Note that the method of calculating the collection efficiency described above is merely an example, and the method is not limited to this method. For example, it is assumed that the spread of the beam 160 follows a Gaussian distribution, but if the spread of the beam 160 is a distribution defined according to the integrated beam current and the beam size, it is assumed that the spread of the beam 160 follows a Lorentzian distribution, etc. good too.

Further, for example, instead of the method of calculating the collection efficiency from the theoretical formula (4), a method using a collection efficiency table showing the relationship between the dose rate and the beam size σ and the collection efficiency may be used. In this method, the CPU 707 of the irradiation control device 108 calculates collection efficiency by referring to a collection efficiency table created in advance.

FIG. 9 is a diagram showing an example of a collection efficiency table. The collection efficiency table 900 shown in FIG. 9 is a matrix-type table in which rows correspond to dose rates and columns correspond to beam sizes, and each element corresponds to its own row and column. represents

The method of creating the collection efficiency table is to perform measurement with the dose monitor 202 for a beam with a known dose rate and beam size, and compare the ideal dose rate with the measured dose rate to obtain the collection efficiency. A method of repeatedly executing the calculation process while changing the dose rate and the beam size can be used.

Returning to the description of the operation with reference to FIGS. 7 and 8. FIG. When the process of step S805 is completed, the CPU 707 of the irradiation control device 108 multiplies the pulse frequency of the pulse signal from the dose monitor control device 206 by the reciprocal of the collection efficiency, thereby obtaining a dose rate that takes into consideration the fluctuation of the collection efficiency. Obtain a corrected pulse frequency corresponding to the corrected dose rate. The CPU 707 counts the number of correction pulses corresponding to the correction dose obtained by correcting the measured dose obtained by measuring the dose given to the n-th spot by the collection efficiency by accumulating the correction pulse frequency using the counter 703 (step S806).

The CPU 707 of the irradiation control device 108 determines whether the corrected dose has reached the target dose by determining whether the corrected pulse number has reached the target pulse number read from the memory 701 (step S807). . If the corrected dose has not reached the target dose, the process of step S804 is executed again, and if the corrected dose has reached the target dose, the irradiation dose monitoring process is terminated, and the process of step S606 in FIG. 6 is executed. be.

Next, the effects of this embodiment will be described.

According to this embodiment, dose monitor 202 measures the dose of beam 160 . Position monitor 203 measures the beam size of beam 160 . The irradiation control device 108 calculates the measurement characteristics of the dose monitor 202 based on the dose and beam size of the beam 160, and controls irradiation of the beam 160 to the patient 150 based on the measurement characteristics and dose. Therefore, the irradiation of the beam 160 to the patient 150 is controlled based on the measurement characteristics of the dose monitor 202 calculated from the actually measured dose of the beam 160 and the beam size. can be controlled more precisely.

Further, in the present embodiment, the irradiation control device 108 calculates a corrected dose by correcting the dose based on the measurement characteristics, and when the integrated value of the corrected dose reaches the target dose, the irradiation of the beam 160 is terminated. to run. Therefore, it is only necessary to correct the dose, and the setting of the target dose can be performed in the same way as before, so there is no need to change the processing system. Suppression becomes possible.

Also, in this embodiment, the collection efficiency of the ionization chamber is used as the measurement characteristic of the dose monitor 202 . For this reason, it becomes possible to use a general dose monitor 202, which makes it possible to suppress additional costs.

Next, a particle beam therapy system and an irradiation control device according to a second embodiment of the present disclosure will be described with reference to FIGS. 10 to 12. FIG. Differences from the first embodiment will be mainly described below. In addition, the same code|symbol is attached|subjected to the structure similar to Example 1. FIG.

The overall configuration of the particle beam therapy system 100 of Example 2 is similar to the overall configuration of the particle beam therapy system 100 of Example 1 shown in FIG. However, in this embodiment, the irradiation control device 108 calculates a corrected target dose by correcting the target dose based on the collection efficiency of the dose monitor 202 instead of correcting the dose. The irradiation control device 108 executes termination processing for terminating the irradiation of the beam 160 when the integrated value of the dose measured by the dose monitor 202 reaches the corrected target dose. Calculation of the corrected target dose is performed for each spot, and the collection efficiency used to calculate the corrected target dose of each spot is the beam irradiated to the reference spot, which is the spot that is earlier in the irradiation order than the irradiation spot, which is the spot. 160 dose and beam size. In this embodiment, the collection efficiency of each spot is calculated based on the dose and beam size of the beam 160 applied to the spot that is one spot earlier in the irradiation order than the spot.

If the difference in the characteristics of the beam 160 with respect to the reference spot and the irradiation spot is sufficiently small, the collection efficiency can be calculated with high accuracy also in this embodiment, and highly accurate irradiation control becomes possible. For example, if the periodic fluctuation scale of the beam parameters is longer than the irradiation time for one spot and the difference in beam parameters between adjacent spots is smaller than the difference between the irradiation instruction and the actual irradiation, the beam at the immediately preceding spot By referring to the average values of the parameters, it is possible to calculate the collection efficiency with higher accuracy than calculating the collection efficiency based on the prescription.

The overall flow of treatment processing for treating the patient 150 in this embodiment is the same as the overall flow of treatment processing described using FIG. However, for the first spot to be irradiated with the beam 160 first, the dose and beam size of the beam 160 for calculating the corrected target dose cannot be obtained. Occasionally, additional processing is performed to reduce the effect of dose error delivered to the first spot on treatment quality.

The additional process is a process of determining, as the first spot, a spot that satisfies a predetermined condition from a plurality of spots obtained by dividing the target volume 151 . For example, additional processing determines the first spot based on target volume 151 .

FIG. 10 is a diagram showing an example of the first spot. In the example of FIG. 10 , the first spot is set to the spot 1001 closest to the center of the target volume 151 . In this case, since it is considered that there is no or little normal tissue in the vicinity of the spot 1001, the influence of dose errors on treatment quality can be reduced.

Note that the first spot shown in FIG. 10 is merely an example, and is not limited to this. For example, the first spot may be a spot whose distance from a predetermined organ is greater than or equal to a certain value. Also, the first spot set by an arbitrary method may be further divided into a plurality of finer subdivision spots, and any of the subdivision spots may be reset as the first spot. In this case, it is possible to reduce the target dose for the subdivided spot, so that the dose given to the subdivided spot can be reduced, and as a result, the influence of the dose error on the treatment quality can be reduced. can be done.

The additional processing may be automated by a program of the irradiation control device 108, or may be processing that allows the operator to select by displaying the target volume 151 and each spot.

In the following, the irradiation dose monitoring process (the process of steps S604 to S606 in FIG. 6) in the second embodiment will be described in more detail.

FIG. 11 is a diagram showing a configuration example of an irradiation control system including the irradiation nozzle 103 and the irradiation control device 108. As shown in FIG. FIG. 12 is a flowchart for explaining an example of monitoring processing by the irradiation control system shown in FIG. In the following, irradiation of the beam 160 to the n-th spot will be described as an example.

After starting irradiation of the n-th spot, the overall control device 106 transmits an irradiation start instruction to the accelerator/beam transport system control device 107 and the irradiation control device 108 (step S1201). Upon receiving the irradiation start instruction, the accelerator/beam transport system controller 107 accelerates and emits the beam 160 according to the control instruction data stored in the memory (step S1204).

The CPU 707 of the irradiation control device 108 executes the following steps S1202 and S1203 after receiving the irradiation start instruction and before the accelerator/beam transport system control device 107 emits the beam 160 .

First, the CPU 707 calculates the collection efficiency of the dose monitor 202 based on the average dose rate and average size of the beam 160 irradiated to the previous spot (n-1th spot) stored in the memory 701. (step S1202). The average dose rate is the average value of the dose rate of the beam 160 irradiated to the previous spot, and the average size is the average value of the beam size of the beam 160 irradiated to the previous spot. . Also, the average dose rate is the average value of dose rates that are not corrected based on the collection efficiency. A method of calculating the collection efficiency may be a method using the theoretical formula (4) as in the first embodiment, or a method using a table as shown in FIG.

Note that when n=1, that is, when the beam 160 is applied to the first spot, there is no average dose rate and average size corresponding to the previous spot. Therefore, the CPU 707 may set a fixed value (eg, 1) as the collection efficiency, or may approximate the collection efficiency based on the average dose rate and average size estimated from the prescription.

Subsequently, the CPU 707 reads the target dose of the n-th spot from the memory 701 and calculates a corrected target dose by correcting the target dose based on the collection efficiency. The CPU 707 converts the corrected target dose into a corrected target pulse number converted into a pulse number and sets it in the counter 703 (step S1203).

Then, when the beam 160 is emitted (step S1204), currents detected by the dose monitor 202 and the position monitor 203 during irradiation of the target volume 151 by the beam 160 are controlled by the dose monitor controller 206 and the position monitor control device, respectively. It is converted into a pulse signal by I/F converters 702 and 704 in the device 207 and output. The CPU 707 of the irradiation control device 108 transmits the pulse signal output from the I/F converter 702 to the counter 703 and integrates the number of pulses. In other words, unlike the first embodiment, the present embodiment does not correct the dose rate based on the collection efficiency. Also, the CPU 706 of the position monitor control device 207 calculates the center position and beam size of the beam 160 based on the pulse signal output from the I/F converter 702 (step S1205).

The CPU 707 of the irradiation control device 108 determines whether or not the accumulated pulse number reaches the correction target pulse number for the n-th spot read from the memory 701, so that the dose applied to the n-th spot reaches the correction target. It is determined whether or not the dose has been reached (step S1206).

If the dose has not reached the corrected target dose, the process returns to step S1205. On the other hand, when the dose reaches the corrected target dose, the CPU 705 of the dose monitor control device 206 calculates the average value of the dose rate of the beam 160 irradiated to the first spot as the pre-correction average dose rate, and controls the irradiation. Record in memory 701 of device 108 . Further, the CPU 706 of the position monitor control device 207 calculates the average value of the beam sizes of the beam 160 irradiated to the first spot as the average size, and records it in the memory 701 of the irradiation control device 108 (step S1207). End the process. The pre-correction average dose rate and average size may be collectively referred to as an average irradiation parameter. Also, the pre-correction average dose rate is a name for convenience, and the dose rate is not corrected in this embodiment.

In the above operation, the timing for calculating the average irradiation parameter and collection efficiency is not limited to the timing described using FIG. For example, the average irradiation parameter may be calculated based on the number of pulses integrated up to a predetermined time before the irradiation of the beam 160 ends, or from the irradiation end timing of the beam 160 to the irradiation start timing of the next spot. The collection efficiency may be calculated between

Also, in the above example, the reference spot is the spot immediately preceding the target spot, but the present invention is not limited to this example. For example, the irradiation control device 108 may select, as a reference spot, a spot whose beam parameters are closest to those of the beam 160 that irradiates the target spot, based on the fluctuation trend of the beam parameters of the beam 160 .

Next, the effects of this embodiment will be described.

As described above, according to the present embodiment, the irradiation control device 108 calculates the corrected target dose by correcting the predetermined target dose based on the measurement characteristics, and the integrated value of the dose reaches the corrected target dose. If so, a process of ending the irradiation of the beam 160 is executed. Therefore, as in the first embodiment, it is possible to set the target dose in the same manner as in the conventional case, so that the processing system does not need to be changed. Therefore, there is no need to add or change existing hardware devices, and additional costs can be suppressed.

In addition, in this embodiment, the irradiation control device 108 calculates the corrected target dose for each spot based on the dose and beam size of the beam 160 that irradiates the spot before that spot. Therefore, since it is not necessary to correct the dose of the beam 160 in real time, it is possible to suppress the occurrence of a delay in determining whether to end the irradiation of the beam 160 due to the processing time related to the correction, thereby suppressing unnecessary irradiation. becomes possible.

Also, in this embodiment, the irradiation control device 108 calculates the corrected target dose for each spot based on the dose and beam size of the beam 160 that irradiates one spot more than the spot. Therefore, the corrected target dose can be calculated based on the dose and beam size of the beam 160 that are considered to have the closest characteristics to the beam 160. Therefore, the dose of the beam 160 irradiated to the patient 150 can be more accurately determined. control becomes possible.

Also, in this embodiment, a spot that satisfies a predetermined condition is set as the first spot to be irradiated with the beam 160 first. Therefore, it is possible to reduce the influence on treatment quality due to the irradiation amount error in the first spot.

It should be noted that the present disclosure is not limited to the above embodiments, and includes various modifications. It is not limited to those having all the configurations described. It is also possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Moreover, it is also possible to add, delete, or replace a part of the configuration of each embodiment with another configuration.

100: Particle beam therapy system 101: Accelerator system 102: Beam transport system 103: Irradiation nozzle 104: Treatment table 105: Treatment planning device 106: Overall controller 107: Accelerator/beam transport system controller 108: Irradiation controller 111: Ions Source 112: Injector 113: Synchrotron accelerator 121: Beam path 122: Bending electromagnet 200: Irradiation system 201A, 201B: Scanning electromagnet 202: Dose monitor 203: Position monitor 204: Ridge filter 205: Range shifter 206: Dose monitor controller 207 : position monitor control device 208: scanning electromagnet control device

Claims (11)

A particle beam therapy system that irradiates a subject with a particle beam,
a dose monitor for measuring the dose of the particle beam;
a position monitor for measuring the beam size of the particle beam;
an irradiation control device that calculates measurement characteristics of the dose monitor based on the dose and the beam size, and controls irradiation of the subject with the particle beam based on the measurement characteristics and the dose; particle beam therapy system. The irradiation control device calculates a corrected dose obtained by correcting the dose based on the measurement characteristics, and executes processing for terminating the irradiation of the particle beam when the integrated value of the corrected dose reaches a target dose. , the particle beam therapy system according to claim 1. The target dose is set in advance for each of a plurality of minute regions of the subject to be irradiated with the particle beam,
The irradiation control device sequentially irradiates each of the plurality of micro-regions with the particle beam, and the corrected dose of the particle beam irradiating one of the micro-regions is the target for the micro-region. 3. The particle beam therapy system according to claim 2, wherein when a dose is reached, a process of terminating the irradiation of the particle beam to the minute area is executed. The irradiation control device calculates a corrected target dose obtained by correcting a predetermined target dose based on the measurement characteristics, and restarts irradiation of the particle beam when the integrated value of the dose reaches the corrected target dose. 2. The particle beam therapy system according to claim 1, which executes a termination process. The target dose is set in advance for each of a plurality of minute regions of the subject to be irradiated with the particle beam,
The irradiation control device sequentially irradiates the particle beam onto each of the plurality of micro-regions, and the dose of the particle beam irradiating one of the micro-regions is the correction target for the micro-region. 5. The particle beam therapy system according to claim 4, wherein when a dose is reached, a process of terminating the irradiation of the particle beam to the minute region is executed. The irradiation control device determines the corrected target dose for each micro-region based on the dose and the beam size of the particle beam applied to the micro-region before the micro-region in the order of irradiating the beam irradiation. 6. The particle beam therapy system according to claim 5, which is calculated by wherein the irradiation control device calculates the corrected target dose for each micro-region based on the dose and the beam size of the particle beam applied to the micro-region that is one step earlier in the irradiation order than the micro-region. Item 7. The particle beam therapy system according to item 6. 6. The particle beam therapy system according to claim 5, wherein said irradiation control device determines a minute area to be irradiated with said particle beam first based on a target volume which is an irradiation area irradiated with said particle beam. the dose monitor is an ionization chamber;
2. The particle beam therapy system according to claim 1, wherein said measurement characteristic is collection efficiency of said ionization chamber. An irradiation control device connected to a dose monitor for measuring the dose of a particle beam irradiated to a subject and a position monitor for measuring the beam size of the particle beam,
calculating measurement characteristics of the dose monitor based on the dose and the beam size;
An irradiation control device that controls irradiation of the subject with the particle beam based on the measurement characteristics and the dose. An irradiation control method by a particle beam therapy system that irradiates a subject with a particle beam,
measuring the dose of the particle beam;
measuring the beam size of the particle beam;
calculating a measurement characteristic for measuring the dose based on the dose and the beam size;
An irradiation control method for controlling irradiation of the subject with the particle beam based on the measurement characteristics and the dose.

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